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LAWN PENNYWORT: A NEW WEED 




ALBERT A. HANSEN 


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Agronomist in Wfod Investigations 




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UNITED STATES DEPARTMENT OF AGRICULTURE 




DEPARTMENT CIRCULAR 165 




Contribution from the Bureau of Plant Industry 




(Office of Forage-Crop Investigations) 




WM. A. TAYLOR. Chief 




Washington, D. C. , April, l')2l 



WASHINGTON : QOVERNMENT PRINTINQ OFFICE : 1921 



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I '-^.'ARy of CONGHtSb 

OCT 3 1933 






LAWN PENNYWORT: A NEW WEED. 



CONTENTS. 



Introduction into the United States- 
Dfscription 



Page. 
3 

4 



Page. 



Distribution 
Eradication- 



INTRODUCTION INTO THE UNITED STATES. 

A number of years ago a plant ^ from southern Asia grew in 
greenhouses in the United States, During the period from 1890 to 
1895 it found some use as a border plant and for flat bedding pur- 




FiG. 1. — Lawn grass being crowded out by lawn pennywort, Wasliington, D. C. 

poses; On account of its outdoor use the plant spread and infested 
near-by lawns, in which the species became very aggressive and 
abundant (fig. 1). 

' Known scientifically as Hydrocotyle rotundifolia. The species was first mentioned by 
William Roxburgh in Hortus Bengalensis, p. 21,. 1814, and later described by him in 
Flora Indica, vol. 2, p. 88, with the notation that the species grew wild in the Botanic 
Gardens at Calcutta, India, being especially abundant during the rainy season. Among 
gardeners in this country it was erroneously called Sihthorpia europea. 

29730 °— 21 S 



4 Department Circular 165, U. S. Depl. of Agriculture. 

It is particularly undesirable on golf greens, where it is readily 
disseminated by the seeds adhering to the shoes of players, especially 
following rains, when the ground is muddy. Large patches of the 
plant which recently appeared on the golf greens of the Washington 
Country Club, near Washington, D. C, not only damaged the turf 
but were also obnoxious because the weed became infested with a 
fungus that caused the diseased areas to become slimy and disagree- 
able. The fungus did not eradicate the weed. 

On account of its comparatively recent introduction into the 
United States and because the plant has become abundant only dur- 
ing the past few years, it does not as yet possess a generally accepted 
common name. Several closely related species are known as water 
pennyworts. On account of its habit of growing on lawns, the name 
laAvn pennyAvort seems appropriate, and is therefore suggested as the 
common name. 











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Fig. 2. — Lawn pennywort (Uydrocotyle rotundifolia) . 1. The creeping stem, showing 
the leaves and seed heads. Note the tufts of fibrous roots originating at the nodes. 
(Natural size.) -2. A single .seed head, showing the compact mass of fruits at the 
end of the seed stalk, characteristic of the species. Closel.v related species either have 
fruits possessing individual stalks or else the clusters are scattered along the entire 
seed stalk. 

DESCRIPTION. 

Lawn pennywort is a creeping i:)erennial (fig. 2), growing typically 
in dense patches (fig. 3). The slender stems not only creep along 
the surface of the soil, but they also grow a short distance below the 
soil surface. The mass of closely interwoven stems enables the plant 
to live over winter. Small tufts of slender, fibrous roots occur at 
the nodes (fig. 2), which are distributed at intervals on the creeping 
stem. The leaves and flowering stalks also grow from the nodes. 

A tiny cluster of white flowers terminates each flowering stalk. 
The flowers appear during early summer and are soon replaced by the 
disk-shaped seeds, which somewhat resemble the seeds of wild pars- 
lev. althou<rh considerablv smaller. 



Lawn Pennywort: A New Weed. 5 

The leaves are shield shaped, shiny, and smooth, each possessing a 
slender stalk arising directly from the creeping stem. The leaves 
vary from one-fourth to three-fourths of an inch in diameter. 

There are seven species of pennyworts occurring in the United 
States. The lawn pennywort can be distinguished from all the 
others by the fact that the flowers and seeds occur in compact clusters, 
one cluster at the terminus of each flowering stalk. In the other 
species, each flower either possesses its own separate stalk or else the 
clusters occur at intervals along the flowering stalks. 

In the open, lawn pennywort grows abundantly in sunny situa- 
tions. In greenhouses it thrives in the shade of the benches. On 




Fig. 3. — A compact mass of lawn pennywort, showing the character of the foliage and 
the small fruiting heads. The lawn grass apparently has all been crowded out by 
the vigorous growth of the wiH>d. (Natural size.) 

account of its ability to grow in the shade, experiments were made to 
determine whether the plant could be used in shady situations, such as 
under large trees and in the shade of buildings where lawn grasses 
refuse to grow. Both transplanting the sod of lawn pennywort and 
the sowing of seeds in the spring failed to produce a stand of the 
plant in densely shaded places out of doors. 

DISTRIBUTION. 

Lawn pennywort is widely distributed in the District of Columbia, 
where it infests lawns, golf courses, and greenhouse beds. The plant 
is also prevalent in the vicinity of Philadelphia and Pocono Lake, 
Pa., and is a pest in Cave Hill Cemetery, Louisville, Ky~., where it is 
said to have been introduced by florists. 



6 Department Circular 165, U. S. Dept. of Agriculture. 

Although its present distribution is somewhat limited, lawn penny- 
wort seems to be increasing its range rapidly. Unless the plant is 
eradicated on its first appearance in new localities it bids fair to be- 
come one of the worst laAvn weeds in the eastern United States. 

ERADICATION. 

Lawn pennywort occurs on lawns in compact patches. When the 
weed first appears, the patches should be dug out with a spade and 
all the plants either burned or otherwise destroyed. It should be re- 
membered that if the removed plants are simply cast aside they are 
likely to mature seeds in a short time, and these seeds may cause a 
new infestation of the weed. The bare spots in the lawn should be 
either resodded or else fertilized and seeded to good lawn grasses. 

Experiments to eradicate lawn pennywort by spraying with solu- 
tions of common salt, arsenic, and iron sulphate and with gasoline 
have proved unsuccessful. All the sprays mentioned killed the 
leaves, but the creeping stems 'were only slightly harmed and soon 
sent up a new crop of leaves. 

The leaves grow so close to the surface of the soil as to escape the 
lawn mower. If it is desired to eradicate the plant by means of 
cultivation, a cultivator of the revolving, scraper type is very efficient. 
With large areas of infestation it is sometimes more practicable to 
spade up the lawn and reseed it. Before reseeding, however, the lawn 
should be allowed to remain fallow for at least two weeks, during 
which time the land should be stirred with a rake occasionally in 
order to induce the germination of any pennywort seeds that may be 
in the soil, and the resulting seedlings should be destroyed with a hoe. 
Unless this is done, the weed is likely to start growth ahead of the 
grass and crowd it out. Encouraging the lawn grasses by fertiliza- 
tion and occasional reseeding will aid in keeping the weed in check, 
but will not eradicate the pest, on account of the pennywort's virile 
growth. 

It is of primary importance to eradicate lawn pennywort when it 
first appears on the premises. Owners of lawns, particularly in the 
regions in which the weed is known to occur, should be on the lookout 
for the plant and should not allow it to obtain a foothold. Pre- 
ventive measures are far more effective than control methods. 

If the lawn is heavily infested it may be desirable to allow the lawn 
pennywort to grow, since it is a rather handsome plant. It has the 
disadvantage of dying down in winter, thus leaving bare spots in the 
lawn. This disadvantage may possibly be overcome by sowing a 
quick-growing grass in the early fall, using one that will remain 
green over winter. For this purpose, redtop may be used in the 
Northern States and Italian rye-grass in the Southern States. 



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